Application of thermally expanded graphite for the cementation of cesium- and tritium-containing waste oils

Abstract

Thermally expanded graphite (TEG) may be used for solidification of radioactive waste oils produced by the nuclear industry. TEG synthesized within the scope of this work retains the properties of a loose powder-like material when saturated with oil at the ratio of 20 g of oil per 1 g of TEG. At this ratio, the effect of wetting of the cement particles with oil, inhibiting the formation of a monolithic structure, is not manifested. As a result, the required compression strength of a cement compound is retained at the oil content of up to 27 vol %. The effective diffusion coefficients of ₁₃₇Cs and tritium are calculated on the basis of the experimental data on leaching. For the compounds without additives, these diffusion coefficients are (1.4–1.6) × 10⁻¹³ m²/s for both radionuclides. The reason for the coincidence of the diffusion coefficients is the nature of molecular motion inside the winding transport pores of TEG determined by its structure. The diffusion coefficients decrease with time for tritium. The leaching rate of ₁₃₇Cs does not exceed the value specified by GOST for the addition of bentonite to the compound in the amount of 6% by weight of the cement. Application of other mineral and organic additives does not give the desired effect and even increases the leaching rate. The leaching rate of tritium does not depend on additives (including bentonite).